Automatic length adjustment of helical springs during coiling



Feb. 18, 1969 s. M. RIMMER 3,427,838

AUTOMATIC LENGTH ADJUSTMENT 0F HELICAL SPRINGS DURING COILING Filed Sept. 28, 1966 I i 64 L524 I i 5 66 r HI W, i f: 70 .H. G 6

STANLEY M- RIMMER BY 1W fmflu. 1- A6 M ATTORNEYS United States Patent 3,427,838 AUTOMATIC LENGTH ADJUSTMENT 0F HELI- CAL SPRINGS DURING COILING Stanley M. Rimmer, Bristol, Conn., assignor to Associated Spring Corporation, Bristol, Conn., a corporation of Delaware Filed Sept. 28, 1966, Ser. No. 582,571 US. Cl. 72-15 Int. -Cl. B21h 37/04, 39/02; B21f 3/10 5 Claims ABSTRACT OF THE DISCLOSURE This invention relates broadly to the spring making art and, more particularly, to the manufacture of helical compression and extension springs.

In the usual method of manufacture of such springs wire is forced against a coiling point and is thereby formed into helical shape. Associated with the coiling point is a device known as a pitch tool which, by proper adjustment across the coiling point and transversely of the direction of movement of the wire, sets the pitch of the helix in accordance with the pre-determined design of pitch and length of the spring, it being understood that all springs are designed in pitch and length to accommodate them to the apparatus in which they are to operate.

It is often necessary that helical springs conform exactly to a pre-determined, designed free length, this being of great importance, for example, when the spring is to be used as a valve spring in an internal combustion engine. However, it often happens that for various reasons, such as variations in the hardness of the wire, a finished spring will vary from the designed free length and must be rejected as not being useful for its intended purpose. In the prior art at least two principal methods have been proposed for eliminating or reducing the incidence of over-length and under-length springs. One of these is to provide switch means spaced from the coiling point by a distance equal to the designed free length of the spring and operable when engaged by the advancing free end of r the spring which is being coiled to operate cut-off means to sever the formed spring from the Wire. In the other of these methods means are provided which are responsive to the formation of an under-length or over-length spring to the effect an adjustment of the coiling mechanism to cause the next spring to be wound to the designed length.

While both of these known methods are useful, it will be observed that neither of them is operative while a spring is being coiled in order to adjust the pitch in such a way as to cause the spring being coiled to be wound with the designed pitch and to the designed length, and it has been the principal object of this invention to provide means and apparatus for solving the problem of overlength and under-length formation in this way.

The invention is described in the following specification and is illustrated in the accompanying drawings in which:

The single figure is a side elevational view of appa- 3,427,838 Patented Feb. 18, 1969 ratus for coiling wire into helical springs and for adjusting the length of each spring during coiling.

By this invention there is provided means which moves with, and in alignment with, the advancing free end of each helical spring which is being wound and which is responsive to any departure of such free end from a predetermined position, which depends on the designed free length of the spring at each increment of its length, to adjust the pitch tool of the forming mechanism to compensate for any such variation, thereby causing the spring to be wound at all times in accordance with its design and, when completed, to have the designed pitch along its length and the designed free length. In the drawings forming part of this specification there is illustrated apparatus for performing these operations, and such means comprise first a machine for forming wire into successive separate helices. This machine is not shown in full in the drawings, being conventional except as described hereinafter, but comprises the coiling point 2 against which wire is forced to be formed into helical shape as shown at 4, and a pitch tool 6 which, by proper adjustment transversely of the coiling point and the wire feed and axially of the helix 4, is operable to control the pitch between adjacent convolutions of the helix which is being formed, These parts are conventional in a spring making machine of the type to which this invention relates.

Means are provided by the invention for adjusting the pitch tool in response to any variation of the free end of the spring being formed from a pre-determined position at each stage of the formation of the spring, and throughout its continual formation, and such means comprise, first, a member positioned adjacent and in alignment with the advancing free end of the spring being coiled, and means for causing such member to move away from the coiling point at a rate and at a distance exactly in accordance with the designed pitch and length of the spring being formed, so that if the spring, as it is being formed, conforms exactly to the designed pitch and free length this member will not be affected by the advancing free end of the spring but, if the spring is being formed either under-length or over-length, will produce a signal causing a corrective operation of the pitch tool to be made.

In accordance with the invention the member which moves with the advancing free end of the spring comprises a target 10 which is positioned in the path of the advancing free end of the spring 4 which is being formed, and in axial alignment therewith. This target is mounted on the lower end of a depending arm 14 which forms part of a linear voltage differential transformer 16 (here inafter referred to as the LVDT) which is slidably mounted on a machine part 18 for movement toward and away from the coiling point 2 in a direction parallel to the axis of the helix 4. Adjacent its upper end the depending arm 14 is mounted at 20 on a part 22 of the LVDT for adjustment in a direction toward and away from the coiling point, and adjacent its upper end it is engaged by the end of an adjusting screw 24 which is operable on adjustment to move the depending arm 14 and target 10 toward the coiling point against the force of a retracting spring 26. The LVDT, in addition to the target plate and its supporting means, comprises a cylindrical winding 28 and a slidable core 30 which is connected to target 10 by a core extension 32 and spring 34.

Means are provided by the invention for moving the LVDT, including the target plate, during the coiling of each spring, from a position adjacent the coiling point to a position removed therefrom. The preferred means for doing this comprise a cam 40 which is mounted on the cam shaft 42 of the coiling machine for rotation therewith, each increment of length of the surface 44 of this cam being designed to correspond to a part of the designed pitch configuration of the spring which is being formed, while the length of the cam surface conforms to the designed free length of the spring. Thus, the point a of the cam surface corresponds to the designed pitch configuration of the first increments of length of the spring, the part b of the cam surface conforms to the pitch configuration of the next increments of length of the-spring, and so forth to the last part c of the cam surface, which conforms to the pitch configuration of the last convolutions of the spring. In this connection, it will be remembered that many springs are so designed that the pitch varies from end to end, automotive valve spring usually having a smaller pitch at the end convolutions than at the intermediate convolutions. A cam follower 46 bears on the cam surface 44 and is connected through lever arm 48 to a pivoted motion transmitting sector member 50 to which is attached one end of a cord, wire or the like 52 which is trained over pulleys 54, 56 and is connected at its other end to the LVDT. The cam follower 46 is mounted in slot 47 in lever arm 48 so that it may be adjusted along the lever arm to vary the effective length thereof.

Means are provided by the invention for translating any variation in the position of the moving free end of the spring 4 which is being wound from its position as determined by the design of the spring, into a movement of the pitch tool 6 which will compensate for such variation. Such means comprise a motor control device 60 the input side of which is connected by leads 62 to the winding 28 of the LVDT and the output of which is connected by leads 64 to the contacts of a reversing stepping motor 66, the armature of which is connected through gearing 68 to the operating lever 70 which adjusts the pitch tool 6 toward and away from the coiling point, whereby the rotation of the motor armature is translated into movement of the pitch tool.

In the use and operation of the described apparatus the surface 44 of the cam 40 is shaped from end to end to correspond at each increment of its length to the designed pitch configuration of a part of the spring, and the length of the cam surface is made to correspond to the designed free length of the spring. This cam is mounted on the cam shaft 42 of the coiling machine and the cam follower 46, which operates the motion transmitting sector member 50, is brought into engagement with it. When the coiling machine is started the position of the cam surface is so adjusted that the LVDT is in its closest position to the coiling point 2. As the coiling machine is operated and the spring is formed the free end thereof advances away from the coiling point, and at the same time the rotation of the cam 40 causes the LVDT to be pulled by cord 52 in a direction to move it away from the coiling point at a rate and for a distance in exact accordance with the designed pitch configuration and length of the spring. If the spring is being formed in exact accordance with its design, as represented by the cam surface 44, the free end thereof will move with the LVDT and will engage the target plate 10 merely sulficiently to hold it against the force of spring 26 in a position in which it is removed from the limit stop 24. If, during coiling, the spring being formed departs in any way from the designed pitch and length, relative movement between the free end of the helix and the core and winding of the LVDT will take place. If the spring is being wound under-length the free end of the spring will retreat toward the coiling point away from the target plate, which will be moved back into engagement with limit stop 24 by spring 26. This movement of the target plate will move the core of the LVDT with respect to the winding thereof, thus generating a negative error signal. If, however, the spring is being wound over-length it will move the target and core into the LVDT to generate a positive error signal. In either case a circuit will be set up through the motor control 60 to operate the motor 66 in one direction or the other to move the pitch tool in such a direction as to compensate for the difference between the actual and designed pitch configuration or length of the spring. Thus, if the spring is being wound under-length, the pitch tool will be so moved by the motor 66 that the pitch being wound into the spring at that instant will be increased, thereby moving the free end of the spring outwardly into the LVDT, thereby de-energizing the motor 66. On the other hand, if the spring is being wound over-length the plus signal through controller 60 to the operating motor 66 will cause the pitch tool to be operated to decrease the pitch of the convolutions being wound at the coiling point, and when this occurs the free end of the spring will move inwardly of the LVDT and the target plate 14 will be again centered in the LVDT, thereby stopping any further movement of the pitch tool in a direction to decrease the pitch.

Because of the adjustable connection of cam follower 46 on lever arm 48 through slot 47, a single cam 40 may be used in making a wide range of springs of different pitch but each of which has uniform pitch throughout its length. This increases greatly the versatility of any machine set-up as springs having different pitches may be wound using a single cam and making adjustment for different pitches merely by adjusting the position of the cam follower 46 along the slot 47 and lever 48.

In the embodiment of the invention which has been described an LVDT is used as the means responsive to variations in the design and length of the spring being coiled from the pre-determined design and length as represented by the cam surface 44. While an LVDT is the preferred means for effecting this function other devices may be used to provide the same function within the scope of the invention. For example, a proximity switch control, or a light source and photoelectric cell, may be used in place of the LVDT.

While I have described and illustrated in this specification one form which the invention may take, it will be understood that other embodiments of the invention, as well as modifications of that disclosed, may be made and practiced without departing in any way from the spirit or scope of the invention, for the limits of which reference must be made to the appended claims.

What is claimed is:

1. In combination with apparatus including a pitch tool for coiling wire into successive separate helical springs, means operable to coil each spring to a pre-determined length, comprising a. target positioned adjacent the pitch tool and in alignment with the moving free end of a spring being coiled, means for moving the target away from the pitch tool at a rate and for a distance determined by 'the designed pitch configuration and free length of the spring at each increment of its length, means responsive to a variation between the movement of the free end of the spring and the movement of the target to adjust the position of the pitch tool to change the pitch of the spring being coiled in an amount necessary to compensate for the variation.

2. Spring coiling means according to claim 1, in which the means for moving the target comprise a movable cam the surface of which from end to end is shaped to conform to the pitch configuration of the spring from end to end the length of which conforms to the designed free length of the spring, and means for transmitting movement of the cam to the target.

3. Spring coiling means according to claim 2, in which the means for transmitting movement of the cam to the target includes a linkage which is adjustable to permit a single cam to be used in the manufacture of springs of different but uniform pitch.

4. Spring coiling means according to claim 1, in which the means for adjusting the position of the pitch tool comprises a reversing motor and means connecting the motor to the pitch tool to move the pitch tool in opposite directions depending on the direction of rotation of the motor.

5. Spring coiling means according to claim 1, in which the means responsive to a variation between the movement of the 'free end of the spring and the movement of the target is a linear vol-tage differential transformer.

References Cited UNITED STATES PATENTS 1,040,196 10/1912 Harter 72-14 1,083,501 1/1914 Lewis 72138 6 7/1928 Bleuel 72135 4/1958 Bache 72-14 US. Cl. X.R. 

